This illustration shows the known rooms of the Great Pyramid, including the Queen's Chamber, the King's Chamber and the long Grand Gallery, along with the newly discovered void, which is depicted as a fuzzy oblong shape.

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Originally published on November 2, 2017 5:53 pm

The Great Pyramid of Giza has been probed with the tools of modern particle physics by scientists who say they have discovered a huge, secret space hidden within its ancient walls.

It is located above a tall, cathedral-like room known as the Grand Gallery, and this newly found space is comparable in size — about 100 feet long, according to a report in the journal Nature.

That makes it a major structure within this royal tomb, which was built around 2500 B.C. and is considered to be one of the Seven Wonders of the Ancient World. Yet until now, despite centuries of study, no one knew this space was there.

"The romantic interpretation and what everyone wants to hear is that this is a hidden room and the king's body is inside or there's grave goods we didn't know about or we're going to learn more about history ... and none of that is responsible speculation at the moment," cautions Peter Der Manuelian, an Egyptologist at Harvard University who was not part of the research team.

"All we know is that we have a void, we have a cavity, and it's huge, which means possibly intentional and certainly worthy of further exploration," Manuelian says, noting that it's not yet clear whether it's a single chamber or more than one.

"In that sense it's obviously frustrating," he says. "On the other hand, as an architectural discovery, something we didn't know about the interior of the Great Pyramid, it's absolutely big news."

Indeed, the team that made the find reports that it is the first significant internal structure found within the Great Pyramid since the 19th century.

Mehdi Tayoubi, with the HIP Institute in Paris, explains that he and his colleagues wanted to investigate the pyramid using the best available non-destructive analytical techniques. They settled on a type of imaging that involves muons, which are tiny particles, like electrons.

"What is strange, for me, is to use those very, very small particles for a huge monument like the pyramid," says Tayoubi.

Muons are made when cosmic rays from deep space hit the atoms of the upper atmosphere. These particles rain down and lose energy as they pass through materials — like the thick stones of the pyramid — and that makes them slow down and decay. By placing muon detectors in strategic locations, researchers can count the number of muons coming through and create a kind of picture that reveals whether the material above is dense, like stone, or an empty space.

Tayoubi explains that his team installed sheets of muon-detecting film in a lower-level room of the pyramid known as the Queen's Chamber. The goal was to test whether they could use muons to accurately discern two well-known rooms located above: the King's Chamber and Grand Gallery.

They saw those rooms but, to their surprise, they found an additional large space as well.

"The first reaction was a lot of excitement, but then we knew that it would take us a long, long time, that we needed to be very patient in this scientific process," says Tayoubi.

Because they didn't want to rely on just one method, they confirmed the find using two other muon-detection techniques.

"The good news is the void is there. Now we are sure that there is a void. We know that this void is big," says Tayoubi. "I don't know what it could be. I think it's now time for Egyptologists and specialists in ancient Egypt architecture to collaborate with us, to provide us with some hypotheses."

He's interested in whether small robots might somehow enter this space through tiny cracks or holes and provide more information.

In the past, before the modern science of archaeology evolved, folks sometimes blasted through walls in the pyramids, says Manuelian.

"That's the good thing about the muon project, there's absolutely no damage to the pyramid at all," says Manuelian. "I hope that, in collaboration with the Egyptian antiquities authorities, further exploration will be set in motion. The study of the pyramids has been going on for an awful long time. So any new contribution is always a welcome addition to our knowledge."

Copyright 2018 NPR. To see more, visit http://www.npr.org/.

ARI SHAPIRO, HOST:

The Great Pyramid of Egypt is one of the Seven Wonders of the ancient world and the only one that's still standing. Now researchers say they've discovered a huge secret space hidden within its walls. NPR's Nell Greenfieldboyce explains that they found it with the help of a subatomic particle.

NELL GREENFIELDBOYCE, BYLINE: The tiny particles used to probe the Great Pyramid are called muons. Muons are created when cosmic rays from deep space hit atoms in the upper atmosphere. The collisions produce muons, which are constantly raining down and passing through everything, everything from your own body to the Great Pyramid of Giza.

MEHDI TAYOUBI: What is strange for me is to use those very, very small particle for a huge monument like the pyramid.

GREENFIELDBOYCE: That's Mehdi Tayoubi. He's a researcher in France who wanted to use the best available modern technology to peer into the Great Pyramid. He knew that muon detectors can be used to create an image of whatever is above them. That's because muons move differently through dense stuff like stone than they do through empty space. So his team put muon detection equipment in a room at the bottom of the pyramid called the Queen's Chamber, and they checked to see if they could use muons to discern the two well-known rooms above, the King's Chamber and the Grand Gallery. They saw both. And what's more, they detected what looked like another large, empty space. That was a big surprise.

TAYOUBI: The first reaction was a lot of excitement. But then we knew that it would take us a long, long time and we - that we needed to be very patient in this scientific process.

GREENFIELDBOYCE: Their patient science paid off because two different muon detection techniques confirmed that this void was really there. The open space is located above the Grand Gallery and is about as big, a hundred feet long. It could be a tunnel or multiple rooms or maybe just empty space left by the builders to reduce the weight of the stone. Whatever it is, the researchers say in the journal Nature that it's the first major feature to be found inside the pyramid since the 19th century.

PETER DER MANUELIAN: As an architectural discovery, something we didn't know about the interior of the Great Pyramid, it's absolutely big news.

GREENFIELDBOYCE: Peter Der Manuelian is an Egyptologist at Harvard University. He cautions that all we know for sure is that there's some empty space.

DER MANUELIAN: So the romantic interpretation and what everyone wants to hear is that this is a hidden room and the king's body is inside or there's grave goods we didn't know about or we're going to learn more about history and all of this. And none of that is responsible speculation at the moment.

GREENFIELDBOYCE: But he says the void is so big it looks intentional. And he thinks it warrants further exploration. Now, in the old days, explorers might have just blasted through the walls to get inside.

DER MANUELIAN: Sometimes, unfortunately, dynamite was actually used before the modern science of archaeology came along.

GREENFIELDBOYCE: He says in these more enlightened times, scientists will surely look for ways to access this space without doing any damage, like slipping tiny robots through cracks or using cameras at the ends of wires. Nell Greenfieldboyce, NPR News.